Ballasted anaerobic system and method for treating wastewater

ABSTRACT

A ballasted anaerobic system for treating wastewater including at least one anaerobic treatment reactor. A weighting agent impregnation subsystem is configured to mix weighting agent with the biological flocs to form weighted biological flocs to create a weighted anaerobic sludge blanket in the at least one anaerobic treatment reactor. A weighting agent recovery subsystem is configured to recover the weighting agent from excess sludge and reintroduce the weighting agent to the weighting agent impregnation subsystem.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/584,545, filed Sep. 8, 2009, which is a continuation-in-partof U.S. patent application Ser. No. 12/008,216, filed Jan. 9, 2008, nowU.S. Pat. No. 7,695,623, issued Apr. 13, 2010, entitled “System andMethod For Enhancing An Activated Sludge Process”, which claims benefitand priority of U.S. Provisional Application Ser. No. 60/879,373, filedJan. 9, 2007, entitled “Process For The Biochemical Treatment OfWastewater”, and also claims benefit of and priority to U.S. ProvisionalApplication Ser. No. 60/994,553, filed Sep. 20, 2007, entitled “AProcess For Enhanced Biochemical Treatment Of Wastewater”, all of whichare incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a ballasted anaerobic system and method fortreating wastewater.

BACKGROUND OF THE INVENTION

One method of treating wastewater, such as wastewater from ethanolplants, breweries, pharmaceutical plants, food processing plants, pulpand paper facilities, and the like, is to use an anaerobic treatmentreactor. The anaerobic treatment reactor is typically seeded with apopulation of microorganisms that ingest contaminants in the influentwastewater to form biological flocs or granules (hereinafter “biologicalflocs”). Wastewater is typically fed into the bottom of the anaerobictreatment reactor and microorganisms consume the waste therein and frombiological flocs. After a sufficient startup period, the biologicalflocs form an anaerobic sludge blanket near the bottom of the anaerobictreatment reactor.

In operation, wastewater is fed into the bottom of the anaerobictreatment reactor and flows upward through the anaerobic sludge blanketbringing the wastewater in contact with the microorganisms that consumethe waste therein. The treated wastewater then flows over the weir ofthe anaerobic treatment reactor as clean effluent.

Conventional anaerobic treatment reactor systems have a limiteddifference in the specific gravity between the anaerobic sludge blanketand the influent wastewater. Therefore, if the flow rate of the influentwastewater is too high, the limited specific gravity difference cancause the sludge blanket to become diffuse. The result may be anelevated loss of microorganisms over the weir which can result incompromised treatment efficiency and system capacity.

BRIEF SUMMARY OF THE INVENTION

This invention features a ballasted anaerobic system for treatingwastewater including at least one anaerobic treatment reactor. Aweighting agent impregnation subsystem is configured to mix weightingagent with the biological flocs to form weighted biological flocs tocreate a weighted anaerobic sludge blanket in the at least one anaerobictreatment reactor. A weighting agent recovery subsystem is configured torecover the weighting agent from excess sludge and reintroduce theweighting agent to the weighting agent impregnation subsystem.

In one embodiment, the weighted anaerobic sludge blanket may beconfigured to treat wastewater and provide a treated effluent. Theweighting agent impregnation subsystem may include an impregnation tankand at least one mixer. The weighting agent impregnation subsystem mayinclude a storage subsystem for storing virgin weighting agent anddispensing the virgin weighting agent into the impregnation tank. Theweighting agent impregnation subsystem may include a venturimixer/eductor. The weighting agent recovery subsystem may include aseparator subsystem for separating the weighting agent from thebiological flocs. The separator subsystem may include a shear mill. Theseparator subsystem may include a centrifugal separator. The separatorsubsystem may include an ultrasonic separator. The separator subsystemmay include a shear mill and a wet drum magnetic separator. Theseparator subsystem may include a shear mill and a centrifugalseparator. The separator subsystem may include an ultrasonic separatorand a wet drum magnetic separator. The separator subsystem may includean ultrasonic separator and a centrifugal separator. The shear mill mayinclude a rotor and a stator, wherein the rotor and/or the statorincludes slots sized as to optimize separation of weighting agent fromthe weighted biological flocs. A majority of the weighting agent mayhave a particle size less than about 100 μm. A majority of the weightingagent may have a particle size less than about 40 μm. A majority of theweighting agent may have a particle size less than about 20 μm. Theweighting agent may include magnetite. The system may include a wastingsubsystem for wasting excess sludge to control the population ofmicroorganisms. The capacity of the system may be increased byincreasing the concentration of microorganisms solids in the anaerobictreatment reactor by reducing the amount of the sludge wasted by thewasting subsystem. The weighted biological flocs may enhance the qualityof the treated effluent by reducing suspended solids and associatedcontaminants therein.

This invention also features a ballasted anaerobic method for treatingwastewater, the method including the steps of: a) receiving influentwastewater in at least one biological reactor, b) forming biologicalflocs in the at least one anaerobic treatment reactor, c) impregnatingweighting agent into the biological flocs to form weighted biologicalflocs to create a weighted anaerobic sludge blanket, and d) recoveringweighting agent from the weighted biological flocs to reintroduce theweighting agent to step c).

In one embodiment, the method may include the step of directing thewastewater through the weighted anaerobic sludge blanket to provide atreated effluent. The method may include the step of separating theweighting agent from the weighted biological flocs. The method mayinclude the step of collecting the weighting agent and recycling theweighting agent to step c). The method may further include the step ofproviding weighting agent in which the majority of the weighting agenthas a particle size less than about 100 μm. The method may furtherinclude the step of providing weighting agent in which the majority ofthe weighting agent has having a particle size less than about 40 μm.The method may further include the step of providing weighting agent inwhich the majority of the weighting agent has having a particle sizeless than about 20 μm. The method may further include the step ofenhancing the quality of the treated effluent by reducing suspendedsolids and associated contaminants therein.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic side-view of one embodiment of the ballastedanaerobic system for treating wastewater of this invention;

FIG. 2A is a schematic side-view showing in one example of a weightedsludge blanket formed at the bottom of the anaerobic treatment reactorshown in FIG. 1;

FIG. 2B is a schematic side-view of the system for treating wastewatershown in FIGS. 1 and 2A depicting one example of an effluent recyclingline and gas collectors;

FIG. 3 is a microscopic photograph showing one example of weightingagent impregnated into biological flocs to form weighted biologicalflocs in accordance with this invention;

FIG. 4 is a schematic side-view showing another embodiment of theweighting agent impregnation subsystem shown in FIG. 1;

FIG. 5A is a schematic side-view of one embodiment of the separatorshown in FIG. 1;

FIG. 5B is a schematic top view showing one example of slots in therotor and stator of the shear mill shown in FIG. 5A;

FIG. 5C is a three-dimensional view of one embodiment of the shear millin FIG. 5A;

FIG. 6 is a three-dimensional front-view of another embodiment of theseparator shown in FIG. 1; and

FIG. 7 is a three-dimensional front-view of yet another embodiment ofthe separator shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

There is shown in FIG. 1 one embodiment of ballasted anaerobic system 10for treating wastewater of this invention. System 10 includes at leastone anaerobic treatment reactor 12, e.g., a bulk volume fermenter (BVF)treatment reactor, an up-flow anaerobic sludge blanket (UASB) treatmentreactor, an internal circulation (IC) treatment reactor, an anaerobiccontactor, a continuous stirred reactor, or similar type reactor.Anaerobic treatment reactor 12 receives flow of influent wastewater 14by line 16. Anaerobic treatment reactor 12 is preferably covered asshown at 13 to create an anaerobic environment therein. Influentwastewater 14 is typically high strength wastewater from ethanol plants,breweries, pharmaceutical plants, pulp and paper facilities, or anysimilar type facilities or plants. Influent wastewater 14 is typicallyfed into bottom 15 of anaerobic treatment reactor 12 by line 16 andflows in an upward direction, as shown by arrows 17. Anaerobic treatmentreactor 12 is preferably seeded with population of microorganisms whichpromotes growth of biological flocs 23. After a sufficient startupperiod, sludge blanket 18 forms near bottom 15 of anaerobic treatmentreactor 12.

To overcome the problems discussed in the Background section above,system 10 includes weighting agent impregnation subsystem 26 whichimpregnates biological flocs 23 to form weighted biological flocs 25,FIG. 2A, to create weighted anaerobic sludge blanket 19. Weighting agentimpregnation subsystem 26, FIGS. 1 and 2A, in one embodiment, includesimpregnation tank 28 and mixer 30 which receives biological flocs fromanaerobic sludge blanket 18, FIG. 1, and/or from weighted anaerobicsludge blanket 19, FIG. 2A, by line 32. Impregnation tank 28 alsopreferably receives virgin weighting agent 33, e.g., from feed hopper 34by line 36, and/or recycled weighting agent 38 from weighting agentrecovery subsystem 74 (discussed below). Mixer 30 mixes the biologicalflocs with virgin weighting agent 33 and/or with recycled weightingagent 38 in impregnation tank 28 to impregnate the weighting agent intothe biological flocs to form weighted biological flocs 25. In oneexample, mixer 30 utilizes a mixing energy which is sufficient toimpregnate the weighting agent into biological flocs to form weightedbiological flocs. FIG. 3 shows a microscopic view of one example ofweighting agent 33, 38 impregnated into biological flocs 23 to formweighted biological floc 25. The weighted biological flocs are then sentback to anaerobic treatment reactor 12 by line 37 and/or line 37′connected to line 16 to form weighted anaerobic sludge blanket 19, FIG.2A.

In operation, influent wastewater 14 is fed into bottom 15 of anaerobictreatment reactor 12 by line 16 and flows upward through weightedanaerobic sludge blanket 19 bringing the wastewater in contact with themicroorganisms that consume the waste therein to provide treatedeffluent 50 which flows over weir 27. In one design, anaerobic treatmentreactor 12, FIG. 2B, may include weirs 60 and 62 which treated effluent50 flows over. Anaerobic treatment reactor 12 may also include one ormore gas collectors 64, 66, and 68 coupled to line 70 which removemethane, carbon dioxide, and other gases generated by the anaerobicprocess of system 10 discussed herein. Treated effluent 50 may berecycled by line 41 to line 16 to maintain a constant upflow velocity inanaerobic treatment reator 12, e.g., as shown by arrows 17. Recyclingtreated effluent 50 may also be used to adjust the flow rate of theinfluent in line 16.

Increasing the density of weighted anaerobic sludge blanket 18, FIG. 1,to form weighted anaerobic sludge blanket 19, FIG. 2A, creates asignificant difference between the specific gravities of the influentwastewater 14 and weighted anaerobic sludge blanket 19. The result issystem 10 can accommodate higher loading rates (flow rate/reactor size)of influent wastewater while preventing weighted sludge blanket 19 frombecoming diffuse. Therefore, system 10 is more efficient and effectivethan conventional anaerobic treatment reactor systems. The weightedbiological flocs in weighted anaerobic sludge blanket 19 also improvethe quality of the treated effluent by reducing suspended solids andassociated contaminants therein.

In one embodiment, the weighting agent may be magnetite, or any similartype weighting agent or magnetically separable inorganic material knownto those skilled in the art which increases the density of thebiological flocs. In one example, the majority of the weighting agentparticles have a size less than about 100 μm. In other examples, themajority of weighting agent particles has a size less than about 40 μm,or the majority of particle size of the weighting agent may be less thanabout 20 μm.

Weighting agent recovery subsystem 74 preferably includes separator 78which recovers the weighting agent from the excess weighted biologicalflocs in line 76 and reintroduces (recycles) the weighting agent toweighting agent impregnation subsystem 26. Weighting agent recoverysubsystem 74 may include recovery subsystem 83, e.g., a wet drummagnetic separator or similar type device, which recovers the excessweighted biological flocs processed by separator 78. Recovery subsystem83 reintroduces recovered weighting agent 38 to weighting agentimpregnation subsystem 26.

System 10 also preferably includes wasting subsystem 85 which wastes theexcess sludge in line 76 generated by weighting agent recovery subsystem74 by line 87 to control the population of microorganisms in anaerobictreatment reactor 12. In one example, the capacity of system 10 may beincreased by increasing the concentration of microorganisms in weightedanaerobic sludge blanket 19 by reducing the amount of sludge wasted bywasting subsystem 85.

System 10, FIG. 1, may also utilize weighting agent impregnationsubsystem 26′, FIG. 4, where like parts have been given like numbers. Inthis example, weighting agent impregnation subsystem 26′ includesventuri mixer/eductor 27 with nozzle 31 and funnel 45 which receivesvirgin weighting agent 33, e.g., from tank 34 by line 36, and/orrecycled weighting agent 38 from separator 78. Venturi mixer/eductor 27preferably receives sludge from anaerobic sludge blanket 18, FIG. 1,and/or from anaerobic sludge blanket 19, FIG. 2A, by line 32.

In operation, the velocity of sludge in line 32 is increased throughnozzle 31. Virgin weighting agent 33 and/or recycled weighting agent 38is dispensed into funnel 45 and then enters nozzle 31 by line 39 andtravels downstream to line 37 and/or line 37′ as shown in FIGS. 1 and2A. The widening of line 37, 37′, FIG. 4, shown at 41 induces intimatemixing and entrainment, as shown at 43. This impregnates the virginand/or recycled weighting agent into the biological flocs to formweighted biological flocs. The weighted biological flocs are thenreturned to anaerobic treatment reactor 12 by line 37, and/or line 37′,FIGS. 1 and 2A, to form weighted anaerobic sludge blanket 19, FIG. 2A.

In one design, separator subsystem 78 discussed above may be configuredas shear mill 112, FIG. 5A, which shears the sludge in line 76 toseparate the weighting agent from the weighted biological flocs. Shearmill 112 ideally includes rotor 80 and stator 82. In operation, theexcess sludge in line 76 enters shear mill 112 and flows in thedirection of arrows 180 and enters rotor 80 and then stator 82. Shearmill 112 is designed such that there is a close tolerance between rotor80, FIG. 5B and stator 82, as shown at 93. Rotor 80 is preferably drivenat high rotational speeds, e.g., greater than about 1,000 r.p.m. to forma mixture of weighting agent and obliterated flocs in area 181, FIG. 5A,of shear mill 112. The mixture of weighting agent and obliterated flocsexits shear mill 112 by line 79, as shown by arrows 184. FIG. 5C showsin further detail the structure of one embodiment of shear mill 112.Preferably, rotor 80, FIGS. 5A-5C, and/or stator 82 includes slots whichfunction as a centrifugal pump to draw the excess sludge from above andbelow rotor 80 and stator 82, as shown by paths 182, FIG. 5A, and thenhurl the materials off the slot tips at a very high speed to break theweighted biological flocs into the mixture of weighting agent andobliterated flocs. For example, rotor 80, FIG. 5B, may include slots186, and stator 82 may include slots 188. Slots 186 in rotor 80 and/orslots 188 in stator 82 are preferably optimized to increase shear energyto efficiently separate the weighting agent from the weighted biologicalflocs. The shear developed by rotor 80 and stator 82 depends on thewidth of slots 186 and 188, the tolerance between rotor 80 and stator82, and the rotor tip speed. The result is shear mill 112 provides ashearing effect which effectively and efficiently separates theweighting agent from the weighted biological flocs to facilitaterecovery of the weighting agent.

In another design, separator subsystem 78, FIG. 6, where like parts havebeen given like numbers, may be configured as ultrasonic separator 116.Ultrasonic separator 116 typically includes one or more ultrasonictransducers, e.g., ultrasonic transducer 262, 264, 266, 268, and/or 270,available from Hielscher Ultrasonics GmbH, Stuttgart, Germany, whichgenerates fluctuations of pressure and cavitation in the excess sludgein line 76. This results in microturbulences that produce a shearingeffect to create a mixture of weighting agent and obliterated flocs toeffectively separate the weighting agent from the weighted biologicalflocs in the excess sludge. The resulting mixture of weighting agent andobliterated flocs exits ultrasonic separator 116 by line 79.

In yet another design, separator subsystem 78, FIG. 7, where like partshave been given like numbers, may be configured as centrifugal separator118. Centrifugal separator 114 typically includes cylindrical section302 located at the top of hydrocyclone 300 and conical base 304 locatedbelow section 302. The excess sludge in line 76 is fed tangentially intocylindrical section 302 via port 303. Smaller exit port 306 (underflowor reject port) is located at the bottom of conical section 304 andlarger exit port 308 (overflow or accept port) is located at the top ofcylindrical section 302.

In operation, the centrifugal force created by the tangential feed ofthe sludge by port 303 causes the denser weighting agent to be separatedfrom the biological flocs in the excess sludge. The separated weightingagent is expelled against wall 308 of conical section 304 and exits atport 306. This effectively separates the weighting agent from theweighted biological flocs. The recovered weighting agent 38 exits viaport 306 and may be deposited to weighting agent impregnation system 26,26′, FIGS. 1 and 4. The less dense biological flocs remain in the sludgeand exit via port 308 through tube 310 extending slightly into the bodyof the center of centrifugal separator 118.

Although as discussed above, separator subsystem 78 may be configured asa shear mill, an ultrasonic separator, or a centrifugal separator, thisis not a necessary limitation of this invention. In other designs,separator subsystem 78 may be configured as a tubular bowl, a chamberbowl, an imperforate basket, a disk stack separator, and the like, asknown by those skilled in the art.

In the example above where a separator 78, FIGS. 5A-5C, is configured asshear mill 112 to create the mixture of weighting agent and obliteratedbiological flocs, a wet drum magnetic separator or centrifugal separator118, FIG. 7, may be used to recover the weighting agent therefrom.

In the example where separator subsystem 78, FIG. 6, is configured as anultrasonic separator 116 to create the mixture of weighting agent andobliterated biological flocs, a wet drum magnetic separator orcentrifugal separator 118, FIG. 7, may be used to recover the weightingagent therefrom.

The result of recovering and recycling the weighting agent as discussedabove with reference to FIGS. 5A-7 significantly reduces the operatingcosts of wastewater treatment system 10.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments. Other embodiments will occur to those skilled inthe art and are within the following claims.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicantcannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

1. A ballasted anaerobic system for treating wastewater comprising: atleast one anaerobic treatment reactor; a weighting agent impregnationsubsystem configured to mix weighting agent with the biological flocs toform weighted biological flocs to create a weighted anaerobic sludgeblanket in the at least one anaerobic treatment reactor; and a weightingagent recovery subsystem configured to recover the weighting agent fromexcess sludge and reintroduce the weighting agent to the weighting agentimpregnation subsystem.
 2. The system of claim 1 in which the weightedanaerobic sludge blanket is configured to treat the wastewater andprovide a treated effluent.
 3. The system of claim 1 in which theweighting agent impregnation subsystem includes an impregnation tank andat least one mixer.
 4. The system of claim 3 in which the weightingagent impregnation subsystem includes a storage subsystem for storingvirgin weighting agent and dispensing the virgin weighting agent intothe impregnation tank.
 5. The system of claim 1 in which the weightingagent impregnation subsystem includes a venturi mixer/eductor.
 6. Thesystem of claim 1 in which the weighting agent recovery subsystemincludes a separator subsystem for separating the weighting agent fromthe biological flocs.
 7. The system of claim 6 in which the separatorsubsystem includes a shear mill.
 8. The system of claim 6 in which theseparator subsystem includes a centrifugal separator.
 9. The system ofclaim 6 in which the separator subsystem includes an ultrasonicseparator.
 10. The system of claim 6 in which the separator subsystemincludes a shear mill and a wet drum magnetic separator.
 11. The systemof claim 6 in which the separator subsystem includes a shear mill and acentrifugal separator.
 12. The system of claim 6 in which the separatorsubsystem includes an ultrasonic separator and a wet drum magneticseparator.
 13. The system of claim 6 in which the separator subsystemincludes an ultrasonic separator and a centrifugal separator.
 14. Thesystem of claim 7 in which the shear mill includes a rotor and a stator,wherein the rotor and/or the stator include slots sized as to optimizeseparation of weighting agent from the weighted biological flocs. 15.The system of claim 1 in which a majority of the weighting agent has aparticle size less than about 100 μm.
 16. The system of claim 1 in whicha majority of the weighting agent has a particle size less than about 40μm.
 17. The system of claim 1 in which a majority of the weighting agenthas a particle size less than about 20 μm.
 18. The system of claim 1 inwhich said weighting agent includes magnetite.
 19. The system of claim 2in which the weighted biological flocs enhance the quality of thetreated effluent by reducing suspended solids and associatedcontaminants therein.
 20. The system of claim 1 further including awasting subsystem for wasting excess sludge to control the population ofmicroorganisms.
 21. The system of claim 18 in which the capacity of thesystem is increased by increasing the concentration of microorganismssolids in the anaerobic treatment reactor by reducing the amount of thesludge wasted by the wasting subsystem.
 22. A ballasted anaerobic methodfor treating wastewater, the method comprising: a) receiving influentwastewater in at least one anaerobic treatment reactor; b) formingbiological flocs in the at least one anaerobic treatment reactor; c)impregnating weighting agent into the biological flocs to form weightedbiological flocs to create a weighted anaerobic sludge blanket; and d)recovering weighting agent from the weighted biological flocs toreintroduce the weighting agent to step c).
 23. The system of claim 22further including the step of directing the wastewater through theweighted anaerobic sludge blanket to provide a treated effluent.
 24. Themethod of claim 22 further including the step of separating theweighting agent from the weighted biological flocs.
 25. The method ofclaim 22 further including the step of collecting the weighting agentand recycling the weighting agent to step c).
 26. The method of claim 22further including the step of providing weighting agent in which themajority of the weighting agent has a particle size less than about 100μm.
 27. The method of claim 22 further including the step of providingweighting agent in which the majority of the weighting agent has aparticle size less than about 40 μm.
 28. The method of claim 22 furtherincluding the step of providing weighting agent in which the majority ofthe weighting agent has a particle size less than about 20 μm.
 29. Themethod of claim 22 further including the step of enhancing the qualityof the treated effluent by reducing suspended solids and associatedcontaminants therein.